The present invention relates to a method and apparatus for automatically punching predetermined hole patterns at precise locations in sheets of material, and more particularly to a method and apparatus for automatically punching predetermined hole patterns at precise locations in printed circuit boards and sheets of material used in the manufacture of printed circuit boards.
A single layer printed circuit board consists of an insulating sheet of material which has a metallized circuitry pattern formed thereon. It is desirable to punch a pattern of holes in the printed circuit board at a precise location with respect to the metallized circuitry so that electronic components may be automatically mounted in various positions on the board by making reference to the precisely positioned holes in the board. The holes may also be used for other alignment purposes.
A multilayer printed circuit board consists of a plurality of interleaved laminate sheets of material, each of which usually has a metallized circuitry pattern on each of its two sides. A multilayer board is manufactured by a process having two basic steps. First, a desired circuitry pattern is formed on each side of each laminate sheet of material to be incorporated in the multilayer board. Second, the laminate sheets of materials having the metallized circuitry formed thereon are interleaved with insulating sheets of material, and then all the sheets are subject to high temperature and pressure in order to bond them together to form the multilayer board.
It is important that the laminate layers making up the multilayer printed circuit board be precisely aligned, or "registered," at the time they are bonded together. To this end, prior to bonding, a predetermined pattern of alignment holes is punched in each laminate layer, and then all the laminate layers are registered via their alignment hole patterns while being bonded together. As a result, each circuitry pattern in the finished multilayer circuit board will be properly registered. Otherwise, the multilayer board may not function properly.
Circuitry is formed on single layer printed circuit boards and laminate sheets of material used in multilayer boards by a conventional photoetching process. In this process, a sheet of material called a photoprint film is placed over a sheet of insulating material having a copper coating on each of its sides covered by a photosensitive emulsion layer. The photoprint film, depending upon the particular process used, has either a negative or a positive photographic image of the desired circuitry pattern which selectively passes ultraviolet light. When the photosensitive emulsion layer on the insulating sheet is exposed to ultraviolet light through the photoprint film, the emulsion layer is selectively hardened so that the remaining unhardened emulsion can be washed away from the copper surface on the insulating sheet. At this point, the portions of the copper surface which are not covered by the hardened emulsion can be chemically washed away so that the desired copper circuitry pattern remains on the sheet of insulating material.
When circuitry is formed on both sides of an insulating sheet of material, a pair of photoprint films is used, one film being placed on either side of the sheet of material on which the circuitry will be formed. It is necessary to register the two films during the photoetching process so that the metallized circuitry patterns so produced will also be registered. To this end, a predetermined hole pattern is punched in each photoprint film at a precise location with respect to the image of the circuitry pattern on the film, and then the two films are aligned via their hole patterns so that their respective circuitry images are in registration.
Thus, as described above, it is desirable and sometimes necessary to punch hole patterns at predetermined locations in printed circuit boards, laminate sheets of material used in multilayer circuit boards, and photoprint films used in connection with the manufacture of printed circuit boards. In the past, systems have been used to accomplish the punching of holes at precise locations in sheets of material. One such system is described in U.S. Pat. No. 4,481,533. However, this system is a complicated and expensive system requiring the use of television cameras and television monitors.